1. Field of the Invention
This invention relates to optical recording systems and more particularly to optical recording systems employing more than one light beam.
2. Description of the Prior Art
Magneto-optic recording provides for erasable storage of data. A laser beam is focused onto a spot on the medium and heats the magneto-optic material to a temperature at which the magnetic domain of the medium may be changed. A magnetic field is applied in one of two directions to orient the magnetic domain of the spot in either an upward or downward direction.
The disk is read by focusing a low power polarized laser beam onto the magneto-optic material. The Kerr effect causes the reflected beam's plane of polarization to be rotated either clockwise or counter-clockwise depending on whether the spot has an upward or downward magnetic orientation. The difference in the rotation is detected and represents data ones and zeros.
The typical system today uses one laser with variable power to do both writing and reading. In order to verify the data recorded, the disk must be rotated twice for each track recorded. One revolution is required to write the track and a second revolution is required to read and verify the track just written.
In order to speed up the recording process, direct read after write (DRAW) systems have been proposed. These systems comprise two lasers; one laser to write a track and a second laser to read the track directly after it has been written. Thus, a DRAW system requires only one revolution of the disk to write and verify a track.
A problem with DRAW systems has been that the addition of the second laser greatly complicates the construction of the optical channel. The beams must be spaced close together in order to focus on the same track at the same time and to prevent aberration and truncation (beam obstruction) effects. However, this close spacing makes separation and detection of the beams difficult. Additional optical components and space are often required to achieve the necessary beam separation. What is needed is a DRAW system with a minimum number of components.